Process for removing oil from particulate matter

ABSTRACT

There is provided a process for removing oil from particulate matter comprising mixing an aqueous slurry of the particulate matter with at least one stream of water applied at a pressure of from 0.5 to 100 Mpa, wherein the one or more high pressure water streams expand adiabatically when mixed with the aqueous slurry.

This invention relates to a process for removing oil from particulate matter, particularly inorganic particulate matter, by mixing an aqueous slurry of the particulate matter with high pressure water streams.

Procedures for the separation of oil from water and aqueous solutions are well known and can achieve very high degrees of separation, however the removal of oil from particulate matter, either in the presence or absence of water, is much more difficult and current separation procedures generally result in levels of residual oil contamination that make disposal of the particulate matter difficult and/or hazardous.

Oil contamination of particulate matter frequently occurs in the oil industry, for example sand becomes contaminated with crude oil either at the well-head or on the production rig during oil extraction procedures, and the settling of solid materials during the storage of crude oil generally produces a mixture of sand, silt and clay contaminated with from 5 to 30% crude oil. Waste sludge contaminated with oil is also often produced during refinery operations. Oil contamination may, however, also be a problem in many other industries. For example, in the manufacture of carbon steel the steel is often processed through a strip-mill, in which ingots of steal are rolled. In order to cool the mill, and help lubricate the process, oil and water are sprayed on to the steel, which leads to the production of oily mill scale i.e fine iron particles in the range of 5 to 1,000 microns coated in oil, at an oil concentration range of 0.2 to 30%. Similarly, oily particles of glass may be produced during the large scale manufacture of glass items. Hazardous railway ballast also contains significant levels of oil contamination, as does the waste extracted from oil interceptors that are used, for example, on garage forecourts.

Current procedures for removing oil from particulate matter include the use of centrifuges, in which oil is forced from the solids by rotation of the centrifuge. The resulting water and oil phase is then further treated, either in a centrifuge or in a separate system. Chemicals are often used in this process to act as de-emulsifiers; however most such procedures normally result in residual oil levels of up to 15% in the solid phase.

A second common separation method is the use of re-circulating hydrocyclones, in which contaminated solids are collected in an accumulator before being jet pumped into a cyclone, sometimes with the addition of secondary water. Such procedures are normally batch processes with the solids being re-circulated 6 or 7 times through the cyclone. Under optimal conditions this procedure can achieve residual oil contamination levels of less than 3% in the solids.

A third treatment method is the use of a Denver Attrition cell, in which oil contaminated solids are slurried with water before being sheared by the use of a very fast agitator impeller in a confined tank. A process for oil separation using a Denver attrition cell is disclosed in U.S. Pat. No. 5,047,083. This procedure can achieve residual oil contamination of less than 5% in the solids, but large amounts of energy are required to drive the impeller at sufficient speeds, and high equipment attrition rates, for example due to damage to the impeller, are normally encountered.

The present invention provides a process for removing oil from particulate matter comprising mixing an aqueous slurry of the particulate matter with one or more streams of water applied at a pressure of from 0.5 to 100 Mpa, wherein the one or more high pressure water streams expand adiabatically when mixed with the aqueous slurry.

The process of the present invention is suitable for removing oil from all kinds of particulate matter, particularly hard particulate matter, more particularly hard, inorganic particulate matter. Suitable particulate matter that may be treated by the process of the present invention includes oil contaminated mill scale, tank bottoms, sand, silt, railway ballast, sludge, glass or mixtures thereof. Suitable particulate matter includes particles of from 0.01 to 75 mm.

In general there is no limit to the amount of oil that may be removed from particulate matter by the process of the present invention, however it is particularly convenient for treating particulate matter comprising from 0.1 to 40% by weight, preferably from 0.2 to 30% by weight, oil.

The process of the present invention is suitable for removing all types of oils from particulate matter, particularly fuel oil, diesel and heavy and light crude, as well as lighter oils such as edible or cutting oils.

For the present invention, the oil contaminated particulate matter should be in the form of an aqueous slurry before mixing with the one or more streams of high pressure water. Depending upon the source of the particulate matter, it may already be in the form of a slurry. If it is not in the form of an aqueous slurry, or if further water is required, the oil contaminated particulate matter may be slurrified with water using any conventional techniques and equipment, for example a cutting pump or a tank plus agitator. For the process of the present invention it is preferred that the aqueous slurry comprises 3 to 35% by volume particulate matter, more preferably 5 to 30% by volume, even more preferably 10 to 25% by volume, for example 18 to 25% by volume.

On mixing of the aqueous slurry of the oil contaminated particulate matter with the one or more high pressure water streams the oil is removed from the surface or interstitial pores of the particulate matter principally by attrition and is deposited in the aqueous phase. The particulate matter may then be separated from the aqueous phase using any conventional procedures. Examples of procedures for separation of the particulate matter and the aqueous phase include gravimetric separation in a modified density separator (for example a Trident De-waterer) or a spiral classifier, or by use of a hydrocyclone. Optionally the particulate matter may be further rinsed with water to remove any residual oil contamination depending upon the final limits required.

Following separation, the aqueous phase may be passed to an oil water separator where the oil is recovered and the water may be further treated to remove residual oil contamination. Any conventional procedures may be used for the oil-water separation and further treatment of the water. An example of further treatment of the water following contentional oil separation is the use of a polish system, comprising a de-silter cyclone bank, and the passage of the water through absorption media chosen to remove dissolved and emulsified oils.

After removal of the oil, the water may be recycled for use in slurrying further oil contaminated particulate matter, or may be safely discharged to the environment.

After separation of the aqueous phase from the particulate matter, the particulate matter will preferably comprise less than 10,000 ppm by weight of oil, more preferably 1,000 ppm by weight or less, most preferably 200 ppm by weight or less.

In the present invention, the one or more streams of water are applied to the aqueous slurry of the particulate matter at pressures of from 0.5 to 100 MPa, preferably from 10 to 60 MPa, more preferably from 15 to 22.5 MPa.

In the present invention, the one or more high pressure water streams expand adiabatically when mixed with the aqueous slurry of particulate matter. Adiabatic expansion is a rapid expansion which occurs without energy being converted into heat. Thus in the present invention, the total energy of the high pressure water is applied to the aqueous slurry of particulate matter, producing high levels of shear and speeding the removal of contaminating oil from the surface and interstitial pores of the particulate matter. The process of the present invention principally removes oil from the surface or interstitial pores of the particulate matter by attrition, rather than by causing the oil to be dissolved, and it is therefore not necessary for heated water to be used when carrying out the invention. It is also unnecessary for air to be added to improve mixing when the one or more high pressure water streams are sprayed onto the aqueous slurry.

In the process of the present invention, the high pressure water is preferably mixed with the aqueous slurry of the particulate matter in from 6 to 18 streams, for example 12 streams. The high pressure streams are preferably applied to the aqueous slurry through nozzles having a total spraying surface area of from 0.2 to 10 mm², more preferably from 0.2 to 8 mm², for example 6 to 8 mm².

In the present invention any means of mixing the one or more streams of high pressure water with the aqueous slurry of particulate matter may be used, however it is preferred that this mixing is carried out as the aqueous slurry is passed through a pipe. Suitable pipes will have diameters of from 100 to 250 mm, depending upon the volume of slurry that is to be treated and the average particle size of the oil contaminated particles. Typical tube diameters are 100, 150 and 250 mm. Pipes for use in the present invention may be made of any suitable materials, as long as they are strong enough to contain the pressures involved in the process and to resist abrasion caused by the mixing of the high pressure water streams and aqueous slurry of the particulate matter. Suitable materials include steel, or Duplex steel if the slurry comprises saline water. Any thickness of pipe may be used, for example from 3 mm to 35 mm.

The aqueous slurry of particulate matter is preferably conveyed to the location at which it is mixed with the one or more high pressure water streams by pumping, or by gravity feed when the oil contaminated particulate matter is railway ballast.

Typical flow rates of the aqueous slurry of particulate matter through pipes when carrying out the present invention are from 75 to 20 0m³ per hour. Where the pipe for use in the present invention has a diameter of 100 mm, preferred flow rates are 100 to 120 m³ per hour; for diameters of 150 mm, preferred flow rates are 120 to 150 m³ per hour, and for diameters of 250 mm, preferred flow rates are from 100 to 160 m³ per hour.

When the present invention is carried out by mixing the one or more high pressure water streams with the aqueous slurry of particulate matter in a pipe, the one or more high pressure water streams are preferably projected into the pipe in the direction of flow of the aqueous slurry and at an angle of 22 to 40 degrees to the axis of the pipe, more preferably at an angle of from 25 to 35 degrees to the axis of the pipe, for example at 30 degrees to the axis of the pipe. Alternatively, each of the one or more high pressure water streams may be projected into the pipe in the direction of flow of the aqueous slurry through nozzles having three separate sub-nozzles, the central sub-nozzle projecting a stream at an angle of from 22 to 40 degrees (more preferably 25 to 35 degrees, for example 30 degrees) to the axis of the pipe; and the other two nozzles projecting streams at an angle of from 5 to 15 degrees and from 45 to 60 degrees (for example, 10 degrees and 50 degrees) to the axis of the pipe respectively. In a preferred embodiment the one or more high pressure water streams are each projected into the pipe in the direction of flow of the aqueous slurry as 3 separate sub-streams at angles of 10, 30 and 50 degrees to the axis of the pipe respectively.

Where more than one stream of high pressure water is mixed with the aqueous slurry of particulate matter as it is passed through a pipe, the streams of high pressure water are preferably all projected into the pipe from nozzles arranged concentrically around the perimeter of the pipe.

A typical flow rate for the high pressure water used in the present invention is 8 m³ an hour.

When the present invention is carried out by the mixing of the one or more high pressure water streams and the aqueous slurry of particulate matter in a pipe, it is preferred that at least a portion of the pipe is lined after the point of injection of water with a sacrificial liner or protective sleeve, which may be made of a plastic material, for example HDPE. The liner or protective sleeve may be from 1 to 10 mm thick, more preferably from 3 to 8 mm, for example 6 mm, and may line any length of the pipe, preferably from 100 to 200 mm of the length of the pipe, beginning in the area where mixing occurs (for example, 150 mm of the length of the pipe).

Surfactants and/or chelating agents may be added to the aqueous slurry of particulate matter before it is mixed with the one or more streams of high pressure water in the present invention. These additional materials may be added either before or after the oil contaminated particulate matter is slurrified, or may be added with the water used to form the slurry. Any conventional surfactants and chelating agents may be used, depending upon the nature of the particulate matter and the type and amount of contamination. Surfactants that may be used in the present invention include cationic, non-ionic and anionic surfactants, including alkyloxylates which do not decompose in the presence of phosphoric, hydrochloric or citric acids, and alkyloxylates with a hydrophilic-lipophilic balance in the range of HLB 7-9, for example Emulan P and Purflac. Chelating agents may also be used, and suitable materials include EDTA, as well as blends of weak organic acids and varying forms of EDTA type chemicals.

Where surfactants are used in the process of the present invention, they may be included in the aqueous slurry of particulate matter at a concentration of from 1,250 ppm to 5,000 ppm by volume, preferably 2500-3500 ppm by volume.

Embodiments of the invention will now be described by way of example with reference to the drawings in which:

FIG. 1 is a diagrammatic representation of a mixing pipe for use in the present invention;

FIG. 2 is a schematic diagram of a process of the invention for cleaning oil contaminated sand;

FIG. 3 is a schematic representation of a process of the invention for removing oil contamination from sediments, for example oily mill scale; and

FIG. 4 is a schematic diagram of a process of the invention for removing oil from sand and silt accumulated in crude oil storage tanks.

Referring to FIG. 1, the mixing pipe 1 comprises a steel pipe 3 having a wall thickness of 25 mm and inner walls 5. The inner diameter of the pipe is 150 mm. The central axis of the pipe is indicated by the arrow 7 and, in use, the aqueous slurry of particulate matter is pumped through the pipe 3 in the direction indicated by the arrow 7. The mixing pipe 1 comprises twelve nozzles 9 regularly spaced in a concentric circle around the pipe 3. Each nozzle 9 is connected to a water supply and comprises a nozzle head 11 in the form or a fan nozzle, so that each nozzle head 11 projects three streams of water 13 into the pipe 3 in the direction of flow of the aqueous slurry of particulate matter. The three water streams 13 produced by each nozzle head 11 are each projected into the pipe 3 towards the central axis 7 of the pipe 3 at angles thereto of respectively 50, 30 and 10 degrees. The water is pumped through the nozzles 9 at pressures of from 10 to 60 MPa and the water streams 13 expand adiabatically on entry into the pipe, causing high shearing of the aqueous slurry of inorganic particles.

The walls of the pipe 3 are protected by a layer 15 of HDPE, which is 6 mm thick, positioned on the inner walls 5 of the pipe 3.

An example of a first process of the invention is shown in FIG. 2, which illustrates a process that may be used for removing oil from contaminated sand. The contaminated sand is collected in a hopper 17 and conveyed to a slurry tank 19 where it is mixed with water to form a slurry comprising 17% sand by volume. Optionally, surfactants may be added to the slurry in the slurry tank 19.

The aqueous slurry is pumped from the slurry tank 19 to a mixing pipe 1 as shown in FIG. 1, and high pressure water is pumped through the nozzles 9 of the mixing pipe 1 from a high pressure pump 21. The high pressure water streams expand adiabatically when mixed with the aqueous slurry causing the oil to be stripped from the surface of the sand and suspended (and partially dissolved) in the aqueous phase. After passage through the mixing pipe 1 the water phase and solid phase are separated in a soil separation plant 23. The sand will typically contain less than 0.04% by weight oil and may be disposed of safely as inert material to landfill or recycling into cement. The aqueous phase may then be further treated by passage through an oil water separator 25 and the oil disposed of safely. The remaining aqueous phase may be further treated to remove trace elements of oil by passage through a foam tank 27, a filter press 29, one or more de-silters, 31, a solids filtration apparatus 33, one or more absorption vessels 35, and a granular activated carbon filter (GAC) 37, before passage to a clean water tank 39. The clean water may then be returned to the environment or re-cycled back to the slurry tank 19.

A further example of a process according to the present invention is shown in FIG. 3, which depicts a process for removing oil from particulate matter, for example mill scale. In this process oily mill scale is first passed through a separation cyclone 41 to remove coarse material, and is then passed to a slurry tank 19, where it is slurried with water and, optionally, polyelectrolytes and/or surfactants. The aqueous slurry is then pumped through a mixing pipe 1 of the type shown in FIG. 1, where high pressure water is added at a pressure of from 10 to 60 MPa via a high pressure pump 21. The high pressure water streams expand adiabatically when mixed with the aqueous slurry causing the oil to be stripped from the surface of the mill scale and suspended (and partially dissolved) in the aqueous phase. The mixed aqueous and solid phases are then separated in a clarifier 43, with the liquid phase being passed to a holding tank 45 and the remaining mixed particulate and liquid phases being passed to a spiral de-waterer 47. The water removed via the spiral de-waterer 47 is passed to the holding tank 45, and the particulate matter is dried by passage through a filter press 29, before being disposed of, for example by drying on gravel beds. The particulate matter will generally have oil levels of less than 0.04% by weight. The water passed to the holding tank 45 may be further treated to separate the oil and water phases by passage through one or more de-silters 31, a solids filtration apparatus 33, one or more absorption vessels 35 and a GAC 37. The separated oil is disposed of and the clean water is passed to a tank 39, from which it may be returned to the environment or re-cycled back to the slurry tank 19.

A further process according to the present invention for removing oil contamination from the solid material matter settled out in the bottom of crude oil storage tanks (known as tank bottoms) is shown in FIG. 4. In this process tank bottoms comprising from 5 to 30% by weight crude oil are passed to a slurry tank 19 and mixed with water to form a slurry comprising from 18 to 25% by volume particulate matter. Surfactants and/or polyelectrolytes may also be added to the slurry at this stage. The aqueous slurry is then pumped through a mixing pipe 1, as shown in FIG. 1, to which high pressure water is supplied via a high pressure pump 21. The high pressure water streams expand adiabatically when mixed with the aqueous slurry causing the oil to be stripped from the surface of the tank bottoms and suspended (and partially dissolved) in the aqueous phase. The mixed solid and liquid phases are then passed to a hydrocyclone 47 where the sand and silt are removed and disposed of. The sand and silt will typically comprise less than 5% by weight oil. The mixed water and oil are passed from the hydrocyclone 47 to an oil/water separator 49 and the recovered oil is transferred to a recovered oil tank 51, from where it may be further processed. The water phase may be passed through a conventional refinery waste water treatment plant or further treated by passage through one or more de-silters 31, a solids filtration apparatus 33, one or more absorption vessel 35 and a GAC 37. The clean water resulting from this treatment may be discharged to the environment or re-cycled to the slurry tank 19. 

1. A process for removing oil from particulate matter comprising mixing an aqueous slurry of the particulate matter with at least one stream of water applied at a pressure of from 0.5 to 100 MPa, wherein the at least one high pressure water stream expands adiabatically when mixed with the aqueous slurry.
 2. A process as claimed in claim 1, wherein the particulate matter comprises mill scale, tank bottoms, sand, silt, railway ballast, sludge, glass or a mixture thereof.
 3. A process as claimed in claim 1, wherein the particulate matter to be treated comprises from 0.1 to 30% by weight oil.
 4. A process as claimed in claim 1, wherein the aqueous slurry comprises 3 to 35% by volume particulate matter.
 5. A process as claimed in claim 1, further comprising separating the particulate matter from the liquid phase after the step of mixing with the at least one high pressure water stream.
 6. A process as claimed in claim 5, wherein the particulate matter comprises less than 1,000 ppm by weight oil after separation from the liquid phase.
 7. A process as claimed in claim 1, wherein the high pressure water is mixed with the aqueous slurry in from 6 to 18 streams.
 8. A process as claimed in claim 7, wherein the water streams are applied to the aqueous slurry through nozzles having a total spraying surface area of from 0.2 to 10 mm².
 9. A process as claimed claim 1, wherein the at least one high pressure water stream is mixed with the aqueous slurry as it is passed through a pipe having a diameter of from 100 to 250 mm.
 10. A process as claimed in claim 9, wherein the flow rate of the aqueous slurry through the pipe is from 75 to 200 m³ per hour.
 11. A process as claimed in claim 9, wherein the at least one high pressure water stream is projected into the pipe containing the aqueous slurry in the direction of flow of the aqueous slurry and at an angle of 22 to 40 degrees to the axis of the pipe.
 12. A process as claimed in claim 9, wherein the at least one high pressure water stream is projected into the pipe containing the aqueous slurry in the direction of flow of the aqueous slurry through nozzles having 3 separate sub-nozzles, the central sub-nozzle projecting a stream at an angle of from 22 to 40 degrees to the axis of the pipe, and the other two nozzles projecting streams at an angle of from 5 to 15 and from 45 to 50 degrees to the axis of pipe respectively.
 13. A process as claimed in claim 1, wherein at least one of surfactants or chelating agents are added to the aqueous slurry of particulate matter before it is mixed with the at least one high pressure water stream.
 14. A process as claimed in claim 13, wherein the surfactants are added to produce a concentration of from 1,250 ppm to 5,000 ppm by volume before the step of mixing with the high pressure water. 